I had a Mazda 3 once exactly like the Galaxy Gray one shown.
Anyway, I did 5k oil changes on Mobil 1 5w-30 and it was happy. My suggestion on repairs:
Scan the codes for the airbag light. Most likely it is the clock-spring on the drives' side steeringwheel because you have used the hell out of it in 300k miles. If that is what it is, know it is super easy to change on that vehicle. I know that because I once changed my steering wheel to address wear. You can probably get a Clockspring for $60 to $80 if that is what you need. It will take 30 minutes to change and you don't need to index the steering wheel because there is like a hex bolt, so it is notched.
For the paint, just touch-up the rust spots. Where it is faded, sand with some 800 grit sand paper then clear coat those panels with a 2k clear like SrpayMax. Wear a respirator and do it in the garage. An N95 mask is NOT enough. It won't look beautiful, but it will look better than it does not not rust.
Just buy a new headlight. The one that is not foggy can then be polished, so they both look crystal clear and match..
Regarding the TPMS sensors, Discount Tire or American Tire sells sensors for your vehicle for $60. They do NOT charge for the installation or pairing if you are a typical customer of theirs. Otherwise, they will still do it for at most $20 per tire. Let's just say $300 fixes your TPMS problems for 7+ years.
$200 fixes all of your cosmetic issues and your airbag issue if you do the work yourself.
Get the suspension issue diagnosed and corrected. If parts are replaced, do the entire rear and pay for an alignment after. It's worth $500 to $700 to not have a car payment if you plan to drive it another 100,000 miles.